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How could I minimize the take off fuel consumption?
How could I minimize the aircraft total takeoff fuel consumption, taking into account all fuel used from start of take-off roll until reaching a safe altitude?
For example, if I fly  with flap retracted and the runway is long enough to takeoff, does that mean I could use less energy than flying with flap extended, since I have less drag?

I don't understand this question at all, what does minimizing takeoff energy mean?

How about minimizing the total aircraft takeoff power consumption? That is use less energy to accelerate the aircraft and lift it off in air.

The lowest takeoff energy is technically negative.  This can be seen in some hang glider cliff launches.

The question seems pretty clear to me, voted to keep open.

Yes, it is a good question. Besides flap configuration, is a shallow high speed “cruise climb” more fuel efficient than a best rate of climb?

A cruise climb certainly will be easier on the engine, with long term benefits there.  Flaps up, provided runway length and clearances are OK, is generally more fuel efficient.

You need to edit the title to better match the body of the question.  The title says "minimize takeoff energy" which nearly everyone will interpret as minimizing the kinetic energy of the aircraft at the instant of takeoff, but that's not what the question is actually about.  Hence, the close votes--

What do you consider a safe altitude?

@DeltaLima fair question, but the word "safe" is a red herring here. The most efficient climb to any altitude is the most efficient climb to every altitude. In other words, if there is a way to climb most efficiently to 1000', then when passing through 500' it must have been most efficient there as well.

@KennSebesta not at all. You can climb by trading speed for height. Climbing at most economical speed to e.g. 250 ft, followed by a zoom climb to 500 ft and stall speed may get you to 500 ft with the lowest possible total fuel consumption. However, that approach will not get you to 1000 ft in the most efficient way.

I think you may be after the most efficient climb strategy. Taking into account the fuel consumed not only during climb to cruise level, but also until a certain distance from the airport is reached. Climbing steep means that the cruise segment is longer and therefor costs more fuel in cruise segment, climbing shallow reduces the length of the cruise segment reduces the fuel burn in that segment. By comparing the total fuel consumption at a fixed distance down route where the cruise altitude has been reached makes climb strategies comparable.

@DeltaLima I would consider a zoom climb which results in unsustainable flight as cheating and outside the bounds of the question. There are many ways to game the question: an earlier poster points out that launching off a cliff is a great way to gain relative altitude. I think it's important to be fair in our understanding of what the poster is asking.

@KennSebesta the zoom climb I described would not result in unsustainable flight. It would get to the termination altitude in a safe and efficient way, however any further climbing would be not optimal. The whole purpose of my clarification questions is to make sure we understand the boundary and termination conditions the OP is accepting, as there is very little context given to the question. There is nothing unfair about that.

A zoom climb, what we glider pilots would call a pilot-induced thermal, is indeed a fuel- and time-optimal termination of any climb so long as we do not concern ourselves with what happens next. In fact, if the plane is not in a full hammerhead at the peak altitude, then we have not yet achieved peak optimality. To get to this second-order termination of the climb must first build on the underlying first-principles optimality. In lay speak, we have first to get within range of the zoom climb; and how to get there is, presumably, the important question being asked.

I doubt that it's possible to provide a general answer, since it's going to depend on specific details of the aircraft.  And indeed, on the runway surface.  For instance, on a grass runway it might be more efficient to use some flap to get the gear out of the grass sooner.

@jamesqf Then you might wish to explain in your answer how this would affect the condition in the question?

Voting to keep open for the second time.

@Koyovis: As long as the wheels are on the ground, the engine has to overcome rolling resistance in addition to strictly aerodynamic factors.  Grass runways have higher rolling resistance than nice, smooth asphalt or concrete, particularly if the grass is long and/or wet.

Assumptions
It's not specified in the question, so I'll assume that it's a gasoline-powered fixed-wing SEL airplane (aircraft is anything which flies, including balloons, rotarywing, etc...) on a standard climbout from a standard (but looooong) runway, etc... I'm also assuming you can't do exotic things like change the engine compression ratio.
I will also assume that efficiency in this context is only energy consumed per unit height. If we want to define efficiency as energy consumed per unit distance traveled, then the problem moves in a different direction and becomes much more complicated.
In my responses below, please understand that these are first-order effects, but second-order effects can lead to modifications. For instance, maximal efficiency might come at a slightly faster/slower airspeed in order to allow for a slightly faster/slower engine RPM.
Also, in general, fuel is not the important consideration for takeoff. Safety is. It's better to burn a few mL more of fuel and keep the airplane from disaster (which would presumably result in wasting a lot more energy).

Mixture (with important caveat at the end)
The mixture is the biggest control on efficiency. In order to achieve maximal efficiency, you need to run as lean as possible. Preferably lean-of-peak, if this can be done. We're talking 20% savings or more here.
Caveat
If you're not taking off at high altitudes, e.g. in the mountains, don't ever try this if you value your airplane engine's life, and as a consequence your own. The engine needs the enhanced cooling from the rich fuel/air mixture. Only at high density altitudes can/should the engine be run at full power at extremely lean settings.
Throttle
The throttle should be fully open, which will provide the least restrictions to the engine breathing.
RPM
If you have a constant-speed prop, then it should ultimately be run as slowly as possible. This gives maximal time for the burning fuel energy to be extracted, as well as minimizing the number of engine cycles and friction.
The RPM should be advanced at such a speed as to provide peak propeller efficiency for the advance ratio.
Fuel
Use the lowest octane gas you can, as this has more energy content than higher octane. Please note that lower octane increases the propensity of the engine to knock/detonate.
Airspeed
Fly the plane at Vy, which is best climb airspeed. This is the airframe's most efficient operating point.
Flaps
In general, don't use them for optimal efficiency. They increase drag more than the increase lift. That's why we like them on landing because we can come in at a steeper angle of attack.
An argument could be made for rapidly "pumping" the flaps in order to pop the plane off the ground, thus eliminating rolling resistance at an earlier point in the takeoff roll. This technique was employed to great effect at a recent STOL competition.

Sounds like you're trading a bit of fuel savings for higher maintenance costs and potential flight safety. IANAP, but it would make me think long and hard about these practices.

IAP, and I couldn't agree more. Several of these techniques would be things I would only employ in a well-instrumented plane in tightly controlled circumstances. If your goal was to set a world record, though, then safety and costs sometimes take a back seat to optimality. In a samilar vein, Kneivel jumping a motorcycle across the Grand Canyon was the "optimal" way across.

You can do two things:

Use the lowest flap setting you can use.
Reduce power to climb power as soon as you are at your departure climb speed.  When you learn to fly, it's full throttle until you are at least at 1000 ft, but on more complex airplanes it's normal practice to reduce to climb power right after achieving climb speed.  When I was flying floats, I would come back to 24 square right after clearing the water, although this was mostly to reduce noise from supersonic blade tips, to keep neighbour complaints down.

I used to go a little farther than that when I was flying regularly from an uncontrolled airport with an 11000 ft runway.  I would take off using climb power (24" MP), more or less using "flex thrust" like a jet.  I would use 2000 ft of the 11000 ft runway instead of 1000 ft. I probably save a thimblefull of fuel or so, who knows.

Could you go into a little more detail? Your approach seems to directly contradict my approach, but perhaps I'm misunderstanding. For instance, if you throttle back, then you are constricting the intake airflow and induction losses are a major source of inefficiency in engines.

Yes but when you reduce to climb power you can start leaning, plus the carb or injection system may have a high power fuel schedule or circuit because fuel is providing a lot of the cooling at TO power. It's also to go easy on the engine.  Temps and pressures are maxed out, and it's  always better to reduce them.  It's the main reason for flex thrust in jets; to extend engine life. That old saw about engines liking being run hard is nonsense.  No mechanical system last longer when run hard than when run not so hard, as long as it gets regular exercise  I cruise my own airplane at 45-50% power.

Got it. I think the difference is my answer gives "absolute best", with the caveat that you shouldn't expect your engine to live long-- perhaps not even to target altitude-- if you treated it this way. I think your answer is "practical best", which  I tend to follow IRL, cruising a 7ECA at 40-50% power.

I think you’re asking about how to get to a safe height with minimum expenditure of fuel.  As you suggest, the aircraft will generally be more efficient in flight with the flaps retracted, and certainly before liftoff there will be significantly less drag than with full flap.  The downsides are that the takeoff run will be longer, and the takeoff speed will necessarily be higher.  If what you mean to ask includes reaching normal flight conditions, flaps up, cruising height and nominal airspeed, then a flapless takeoff is very likely to use less fuel.  On the other hand, if you consider 10ft to be a safe height and you have an aircraft with small wings and huge flaps then the opposite may be the case.

Last sentence is true but may throw some people off.  But flaps may be needed if weight is a bit high (rather than tiny wings!).

Maybe, but if you can’t take off without flaps then you can’t fly without them.

@Frog: You use the flaps until you burn off enough fuel...

Better surely to set off with a little less fuel?

Configure airports and planes in such a way that take-off catapults, similar to those used on carriers, can be used to accelerate them up to take-off speeds while using less onboard fuel than would otherwise be used.
Note that the greater distance available with such a ground based "catapult" means that the device can act over both a greater distance and longer period of time, which would reduce the strain on the equipment and passengers.
The complexity of this system would be cost prohibitive to set up and maintain, but if you only care about reducing the fuel usage during takeoff, this would do so.
Caveat: I've been reading a lot of worldbuilding posts recently, and this post was likely highly influenced by that.

Better still, build your airport on a steep slope at cruising altitude (I’ve seen a few examples in the French Alps, it’s a real thing).  Land upslope and launch downslope.

Use lighter than air aircraft (aerostat) filled with helium or hydrogen. They have other shortcomings but should not use much energy just for lifting up.


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Could most commercial jet engines today run on ethanol without any problems?
Most commercial jet engines today would be those large jet engines on large passenger craft like a Boeing 747. Can these run on straight ethanol without any problems?
Would more maintenance be required? Would the engine lifetime be reduced? Would it be more susceptible to flameouts or other mechanical risks? Would the airplane never make it off the ground? (I imagine thrust reduction will be limit the takeoff weight.)
One reason I'm asking is because eventually petrol will be gone. (I'm not an apocalyptic saying that will happen next year, but somewhere down the line it will certainly be gone.) Will jet engines require a major redesign, or could they just use ethanol for a few years/decades and be fine?
Note: I'm talking about jet engines (turbofans, but turbojets are okay too), but not piston engines and turboprops.
EDIT: A lot of talk has been generated that ethanol contains less energy than kerosene. I assure you I'm aware of this. Ethanol is like 25 MJ/kg and kerosene is more like 40 or 45. I'm not asking this question with energy efficiencies in mind, but rather out of curiosity if the same engine geometries will work well with both fuels.
A rephrasing: Would current jet engine geometries (blade angles, compression ratios, volumetric flow, etc.) work well with ethanol instead of regular jet fuel?

Probably extensive testing is required. Ethanol can destroy rubber seals and so on. If you want to run a car on ethanol special modification to the fuel system is required

Whether current production engines can run it efficiently/without lots of extra maintenance is a moot point since there's more than plenty oil around to well outlast the lifespan of all current engines. New engines will be designed optimally for the fuels available at the time.

A more likely solution is synthetic jet fuel. The Fischer-Tropsch process was being used for this as far back as WW2, and the US Navy is working on a solution that could be used on nuclear-powered aircraft carriers: http://www.nrl.navy.mil/media/news-releases/2012/fueling-the-fleet-navy-looks-to-the-seas

I want to question the belief that "petrol will be gone" - why would it be? As it gets harder to produce (or more heavily regulated), the price rises. As the price rises it becomes economical to partially replace it with other energy sources, or reduce consumption, or synthesize it (including growing it). At some point extracting it from the ground stops because it's no longer profitable, but we never 'use it all up' and we always have petrol - price goes up, consumption goes down on some kind of curve, just like any other commodity.

No one has yet mentioned a redesign of the combustion components, but my guess is that differences in the fuels' stoichiometric mixture ratios, volatility, viscosity, reaction speed, flame propagation rates and other issues that I haven't thought of would require changes to the nozzles and combustion chambers. The fuel delivery and control system would have to be at least re-calibrated for ethanol, and may not be adjustable to the extent needed.  I know that industrial gas turbines can be run on a variety of fuels, but I believe these components have to be adapted to the fuel.

@Spike0xff yes I know it will deplete as a bell curve and never still be literally all gone. Some will remain trapped and unextractable except at huge costs. I was being simplistic in saying it will be "gone" because this question isn't really about that, but about current engine geometries possibly working with ethanol.

@sdenham Yes exactly. I edited the OP to include a thing about engine geometries.

Although turbines could be designed to run on ethanol it's actually a lousy aviation fuel (actually it's a lousy fuel in general). Petroleum-based jet fuel is high grade kerosene which has lubricant properties, which ethanol lacks, and ethanol has different characteristics which mean you can't pour it in and use it as a replacement.
Some problems with ethanol as a fuel are:

It's a solvent which dissolves some types of seals and hoses
It evaporates very easily, and can cause vapor lock
It is hygroscopic, meaning it attracts and mixes with water very readily. Water contamination would not settle to the lowest point, instead it would be suspended with the fuel
It has significantly less stored energy per unit of weight. Jet fuel has an energy density of 46 MJ/kg (megajoules per kilogram) and pure ethanol has 26.4 MJ/kg; that's only 57% of the energy density of jet fuel! Even if a jet was able to burn it at its maximum efficiency it would get just over half the oomph from it.

There are bio-fuel replacements for jet (and diesel) fuels based on oilseed crops like rapeseed (canola), palm oil, etc. These are processed to remove their OH atoms using transesterification to create fuels which are almost identical chemically. Modifying jets to use ethanol would be hugely expensive if it is even possible to do, so there's no point given there's a suitable replacement.
The point is actually moot though because crop-based biofuels are never going to replace petroleum. There simply aren't enough crops grown to feed people and engines at the same time, in fact even if we used all the worlds farmable land to grow bio-fuel crops instead of food crops we still would not have enough of it to replace fossil fuels. We have enough trouble feeding people already and the biofuels craze is not helping that. Bio-fuels based on non-food crops from marginal land may some day become economically viable and partially replace petroleum fuels.
After some searching I found a link to an article I wrote on biofuels for AOPA UK magazine which goes into more detail on biofuel issues.

Most gasoline around the world is actually a 10 or 15% blend of ethanol, so I'm guessing the "dissolves some types of seals and hoses" issue is not that hard to solve. If I'm wrong, please explain and clarify.

It is not hard to solve - you replace the seals and hoses with newer ones which won't dissolve. Most cars built in the last 20 years have seals which can tolerate 15% ethanol, older cars often don't and end up needing repairs when the seals and hoses degrade. 10-15% ethanol doesn't destroy seals that fast.

..even if we used all the worlds farmable land to grow bio-fuel crops instead of food crops we still would not have enough of it to replace fossil fuels... Do you have a source for that? It is a terrific way to put humanity's dependence on fossil fuels in perspective and I would love to use it.

That statement is based on weeks of my own research, which I put together in a blog article here: http://tetsui.net/gdblog/2011/06/17/why-biofuels-make-no-sense/

Having your own non-scientific research as basis for reference is not really appropriate for such a statement. There are plenty of academic papers on the field.

@user, maybe you should check with GgD on that before just dismissing his statement out of hand - he may be preparing for a peer-reviewed scientific publication, and publishing initial results on his personal blog. (Then again, maybe he isn't.)

@FreeMan, I'm not dismissing bio-fuels at all, I'm saying that you have to have a sustainable source of biomass, and that Ethanol is not a good choice for aviation. If cellulose-based alcohol fuels can be made economic  and algae based diesel produced in quantity then we won't have pressure on food crops. Getting off-topic though

@FreeMan That's only because his engine/fuel system was optimized for the E85. It's a matter of fact that gasoline has more potential energy per unit mass (or per unit volume) than ethanol, so if you're getting more power from the same amount of ethanol blend, it's only because you're burning the normal gas inefficiently. Of course, it's also possible that his fuel system was simply feeding fuel to the engine faster with the Ethanol blend (that site doesn't compare the fuel consumptions for those power figures that I can see.)

@GdD: It doesn't matter whether we have "enough" biofuels, that's a total non-issue. The real limitation is not fuel supply but CO2, and we'll have to reach steady-state quite soon. Part of that can be achieved by replacing fossil fuels with CO2-neutral biofuels, the rest will have to be achieved by cutting back fuel use.

@FreeMan: Another way of looking it is that an engine of a given size will be able to guzzle ethanol faster than gasoline; the amount by which ethanol's maximum feed rate is higher than gasoline exceeds the amount by which its volumetric energy density is lower, allowing engines to produce more power.

It's a question of being able to grow enough biomass and food at the same time @MSalters. There's only so much land and fresh water for traditional biofuel crops, that's why algae-base biomass is so important.

Anither example of what GdD is saying about how growing fuel crops is not a long-term answer: The palm oil crops which are growing at a breakneck pace in southeast Asia are destroying enormous amounts of ancient peattand which ace the best carbon sinks on the planet and take centuries to reform. The net effect of palm oil plantations on CO2 is really bad.

"[Ethanol is] a solvent which dissolves some types of seals and hoses" So, just like kerosene. The salient point is presumably that ethanol might dissolve the seals and hoses of an engine designed to run on kerosene, (just as kerosene might dissolve the seals and hoses of an engine designed to run on ethanol).

@FreeMan a blog post without sources, to be considered as a scientific publication? What am I doing in this world?

@GdD - "It [ethanol] is hygroscopic"... so is kerosene, so what is the point?

Kerosene is a very little bit hygroscopic @jwzumwalt, but the specification for Jet fuel is 30ppm water content. Ethanol blends can have 6000-7000 ppm water content.

@GdD  -I am not sure what you consider a little water... But Jet fuel has enough water for algae and microbes to grow uninhibited in fuel tanks of airliners.

Water can get into any fuel @jwzumwalt, this often happens when tanks cool. Water that can grow algae is less likely to be hygroscopic, more free water which hasn't been absorbed. You have more of that because Jet absorbs less of it.

@TomMcW: That doesn't make it a bad idea; it just means that it's being implemented poorly.

Yes, jet/turbine engines can run on ethanol... but ethanol has only 60% of the energy content per mass unit of Jet-A fuel which means you have to use 67% more of it by mass to get the same energy output.
You'll have to increase the additional fuel carried (due to having to lug around a lot more low density fuel) of every aircraft by quite a margin if you were to fuel them with ethanol.
Alternative energy use for turbine engines has been studied extensively.  The problem is always that they pack much less energy density than Jet-A, making them unfeasible.

Yes I know ethanol has much less energy content and thus is not economical today. I won't downvote since nothing you said was incorrect, but I'm really looking for the details of using ethanol in today's engines, like maintenance changes, not efficiency reduction.

While I guess this answer implies it, it's probably worth explicitly pointing out that carrying all of that extra fuel mass around means that the plane needs to produce more power to remain airborne. Thus, the fuel requirements to move the same payload the same distance in the same amount of time grow superlinearly as fuel energy density decreases. This also generally means more pollution for the same work accomplished.

I'm not an expert of real jet engines. I think it should in general be possible to run a jet on ethanol, though some modification might be necessary. Some materials might not be resistant to ethanol and need replacement.
But the main reason for not using ethanol is that it contains by far less energy: Just 27MJ per kilogram instead of 43MJ for jet fuel.
For the same energy demand (i.e. an entire flight), the aircraft would need 60% more fuel, plus additional fuel to carry the additional fuel...
Here is some data about the A380 from wikipedia (fuel weight calculated by a factor of 0.8kg/l):
Maximum take-off weight    575,000 kg (1,268,000 lb)
Operating empty weight     276,800 kg (610,200 lb)
Max. fuel capacity         256,000 kg (564,000 lb) (44% MTOW)
-------------------------------------------------------------
Calculated payload:        299,000 kg

If the aircraft would use ethanol, this changes to:
Maximum take-off weight    575,000 kg (1,268,000 lb)
Operating empty weight     276,800 kg (610,200 lb)
ethanol equivalent:        407,000 kg (900,000 lb) (70% MTOW)
-------------------------------------------------------------
Calculated payload:       -108,000 kg (-240,000 lb)

Even if you manage to load the additional fuel, the aircraft is waaay to heavy to take off, even without payload.
It's not the cost (or availability), it's the bad energy density which makes ethanol unsuitable.
It would be better to use something more similar to jet fuel like Biodiesel, which is similar to fossile diesel. Biofuels typically also have a lower energy density, but not to an extent that it makes them technically unsuitable.
There are different kinds of such fuels for aviation, and wikipedia has an impressive list of test and commercial flights using biofuels. In most cases, a mixture of fossile fuel and biofuel was used, but on some flights, one engine (or the entire aircraft?) was powered by pure biofuel.
The main problem with biofuel of any kind still is availability. We simply can't produce enough to replace fossile fuels completely.

The straight conversion of fuel for gas engines is a change in air/fuel ratio. Other factors come into play such as fuel supply, lubrication,  corrosion, etc. These are a non-issue in the cars I have converted. One aspect that should be addressed here is the power to weight ratio of the resulting system. You can make more power in a car using the same engine by switching to ethanol. Yes, you have to fill up more often. Yes, there might be something with seals in older cars. Bottom line: it's faster, cheaper, and the exhaust does not stink.
There is a new technique for making ethanol developed by scientists at Oak Ridge National Laboratory that converts  industrial smoke stack exhaust to ethanol. This is a new source for fuel that cleans up pollution at the source while providing a less polluting fuel for use. No grain involved so no impingement on food sources.
NASA is running tests on a new biofuel made from false flax. The Blue Angels are flying 50/50 with this new stuff. The Navy is supposed to be switching over by 2030. I'm calling for that to happen faster. Anyone interested in biofuels should check it out. The plant has never been bred for fuel production so there is an opportunity. Interesting side note, the area around Fukushima is planted with the stuff. Genetic mutations most likely have occurred. Among those mutations will be something that affects fuel production capability.

Welcome to the site and thanks for the info. If you can, post links to reference things.

Yes it is possible to run gas turbines on ethanol, as listed on this site: one of the 25 different types of fuel that the article considers. Some practical re-design of the gas turbine might or might not be necessary:

Lubrication was mentioned, a pretty trivial design issue. Aero gas turbines are used for power generation, often running on LPG or LNG which don't have much lubricating properties either.
Knocking is not an issue in gas turbines either. In reciprocating engines where the fuel/air mixture is compressed knocking can create problems of premature ignition timing. In gas turbines the incoming air is compressed first, and the fuel is injected into the high pressure, high temperature air stream.

NO!  Both as originally asked and revised.  NO!
Maintenance?  Jet-engines are LUBRICATED with their FUEL.  Ethanol does not have the necessary viscosity and lubricity to protect the moving surfaces.  How about replacement after every flight!
The High-bypass fan at the front of the engine requires a certain amount of Shaft Horse Power delivered from the “Jet” portion at the back.  The existing fuel lines can't deliver enough ethanol to achieve either full power or peak efficiency.
Burning ethanol will require re-engineering not limited to:

recirculating oil lubrication pumps
oil coolers (which increase drag)
larger fuel lines
ethanol safe seals

Ethanol's lower density alone does not prevent its use as the vast majority of commercial fights do not take off with full fuel and as such there has always been extra volume available.  However, the longest direct flights such as L.A. to Sydney will require a fuel stop.  Adding extra landings and takeoffs to an existing routes as well as fuel depots almost define the word problem.
Ethanol?    NO!
Peanut oil? Yes

Adding extra landings and takeoffs to an existing routes as well as fuel depots almost the define the word problem. ehum, what? could you clarify?

@Federico current airliners and routes are built around the ability for the aircraft to get from point A to point B on its own fuel tanks - switching to a lower energy density fuel means you can no longer get from A to B on an airliners own fuel tanks (or rather the margins for the route are decreased, potentially past unsafe levels).  This means you have to start thinking about either changing the routes so the aircraft makes a fuel stop part way there, or you build bigger fuel tanks into the aircraft.

@Federico Fuel stops mean more time, more wear and tear and more cost (you have to descend from cruise altitude, depressurise the cabin, land, take off, repressurise and get back to altitude), while bigger tanks mean more weight to carry, meaning more fuel needs to be burned to fly the same distances.

ah, ok. So there is seems to be an extra the in that sentence (the one in front of define)

Real jet engines are not lubricated by fuel. They have a separate oil system which (contrary to reciprocating engines) main purpose is to cool the bearings, only part of its purpose is to lubricate them

As a drop in replacement for everyday use the answer is no, plausible in a one time emergency escape from zombie island yes.
Yes, gas turbines, much like steam engines, can run fairly well on just about anything that makes heat. The issues are more practical in energy density, ease of use and reliability(coal dust may clog or stopping every few minutes to open the combustion chamber and re-stoke a wood fire would not be practical), and engine life.(including deposits) Ethanol specifically is highly erossive to un-coated aluminum and has low energy per mass.
Lubrication issues are primarily in the fuel pump and injection system and could be overcome, a jet turbine spindle had dedicated lube oil and really no other bearings.
Bio-diesel fuels are close to regular petroleum in many ways but they are very strong solvents so need special teflon-like polymers for any non-metal hoses and seals. Also batch consistency of both raw materials and processing is important regarding things like the gel-point and wax crystals, which is important at the -40 of high altitude.
There have been experimental jet engines that used nuclear fuel rods for the heat, typical problems with radiation.

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What type of hydraulic oil is used in the aviation industry?
Among the three different types of hydraulic fluid types (mineral based/petroleum based, synthetic esters, naturally occurring vegetable oils) which one is used in the aviation industry and why?

Define "better". The companies that promote these witches brews generally propose stuff that is as complicated and proprietary as possible, because the more proprietary it is, the more profit everybody makes. Often simple substances are the best choice for the consumer, but nobody makes a profit selling cheap generic materials that anybody can get at a hardware store, like mineral oil. So, are you talking about what is good for the manufacturers or the operators?

Better for what? Brake systems? Ground trucks? This is way too broad.

Way too broad? OP mentions aviation industry, is that not within the scope of the Aviation Stack Exchange?

@Koyovis it's closed as too broad, not off topic.

@fooot Yes I see that. I just cannot see what is too broad about asking which hydraulic fluids are used in the aviation industry. ATA chapter 29 deals with Hydraulic Systems on board of aircraft. Hydraulic systems are used for brakes, flying controls, landing gear extension, engine control etc: they have a broad use in the aviation industry  Like all systems designed for on-board use, there are specific design rules for airborne hydraulic systems, including stipulations on the hydraulic fluids for the aviation industry. OP's question is perfectly valid,

Apparently lemonade is a good choice

General Aviation brakes and gear systems use a mineral based brake fluid that conforms to MIL-H-5606A. Here’s more info. http://us-packaging.com/documents/phillips66/aviation_products/66_5606H_5606A_Avia_fld.pdf

For the aviation industry, flammability is a major concern, and aviation hydraulic systems require Fluids that cannot burn yet don't create corrosion and still lubricate. Skydrol for instance is a phosphate based ester, a nasty substance that irritates the skin, but at least has some flame resistance.
Old hydraulic motion systems on simulators used the stuff, later ones went to mineral oils like Shell Tellus. If there is an oil leak in a pressure hose, a fine mist of fluid droplets appears, flammable if mineral oil but this could be handled in a ground facility with extinguishers everywhere. Not a good circumstance in an aviation accident though, and that is why in aircraft the esters have to be used.
Vegetable oils are not used for hydraulic systems in the aviation industry at this moment as far as I am aware.

It all comes from Swissair Flight 306. That accident moved the authorities to demand only flame resistant hydraulic fluids. By the way, here is more inside info on that accident.

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On the Boeing 737 ND display what does terrain value indicate?
On the Boeing 737 ND display what does terrain value indicate? (e.g. Terr 0016 0032)

On the 777 FCOM, it is written

Upper value of the TERR thing is altitude of the highest object in the selected range of the map
Lower value is the altitude of the lowest object in the selected range of the map

Both of these values are in feet and for example 020 is 2000 feet, 014 is 1400 feet. When any number is in red, or if the terrain is red, it means it is at or above your current altitude.

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How does aircraft valet parking work?
The World Economic Forum is in full swing in Davos. The world's Rich & Beautiful are all GA-flying into ZRH, which is not one of the world's largest airports, and continuing on via helicopter or car.

This is how the parking lot at ZRH looks right now. The runways are at the top right. If the plane at the bottom left wants to leave, we would need to move no fewer than five or six other planes.
How would this work in practice? I can't very well imagine the pilots just handing their keys off at the airport for some "plane valet" to move the plane whenever it's in the way. Are the original pilots on standby in some very close hotel such that every single plane's pilot can on short notice come in to move their plane, or to supervise ground operations moving them?

Pilots (most of them) are not in the "richest" group. The pilot will do maintenance and stay on call. At any moment (withing few hours) there may be change of plan. Note: I'm not sure that is the parking of WEF people, or just the usual GA planes (which are probably not needed) are moved there.

Closely related, the answers here might also help you.

There are no keys to hand off. Most jets don't have any access controls - staff access trumps security.
Except on takeoff, large jets are preferably moved around the airfield by ground tugs, rather than taxiing. Airport staff will tug or taxi the planes to where they need to go, even if the pilot isn't around.
There's no special link between a pilot and a particular hull, the controls are the same. The staff making sure the parking brake is off don't have to be pilots. To give liability a wide berth, the bizjet's operator / captain can be in the loop, but it's not a hard requirement.
Modern towbarless tugs can operate without a pilot or mechanic in the cockpit at all, by lifting the nose wheel.

It's also likely the FBO has a rough idea of when some aircraft are likely to leave.

@ceejayoz - also if someone does wind up leaving "out of order" and they have to pull some other planes out of the way, assuming that the conference has ended or nearly ended they probably wouldn't push the other planes back into the bunch they would just leave them sitting out. It's also possible that the bunching up is only done during the conference when they know that no one is going anywhere, so that the planes take up less room on the ramp. Then maybe as the conference is ending they pull them all apart since they know most of the planes will leave within a few hours.

To Therac's point, airplanes are not valet parked like cars.  General Aviation aircraft operate out of Fixed Base Operators (FBOs) based on an airfield.  These operations provide overnight parking, hangering, maintenance, fuel and other services to aircrews while on the ground.  Once parked and shut down, the aircraft is typically chocked and left with the parking brake off to facilitate towing with a tug or similar airport vehicle.
When there are high volumes of GA traffic to events like this, FBOs may use a section of the ramp belonging to them for transient parking of aircraft.  Generally the ramp is sterile and secure (and if they have a large volume of VIP aircraft, FBOs also employ their own security forces as well as local airport police to protect aircraft under their care.   Most VIPs travel incognito for safety reasons; very few people know about their arrival or departure.  The FBO staff would be in contact with the flight crew and let them know of where their aircraft was parked on the field.  If a flight crew needed an aircraft immediately or had proposed departure time, the aircraft would then be towed from parking to an area on the ramp for pre-flighting, fueling, catering and loading for departure.
Below is a video Discovery networks did about 10 years ago or so on Donald Trump's 757 aircraft, which features the additional difficulties and arrangements for operations from SheltAir FBO at New York's LaGuardia airport.


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RNP 1 vs RNAV(GNSS) STARs GPS Primary Requirement for A320?
1.Do we need GPS primary before enter the RNP 1 airspace and RNAV(GNSS) STARs and SIDs?
2.What will we do if we lose GPS primary function during RNP 1 airspace and RNAV(GNSS) STARs and SIDs?
Thank you

Yes. See FCOM for required equipment for RNP1. In case of RNAV1, at least in my manuals the GNSS is not required. Usually also the chart says explicitly that GPS/GNSS is required for the procedure.
Ask for radar vectors or alternative clearance


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Detail an appropriate report to ATC when entering a holding pattern?
Regarding VOR holding calls, what should be included in the initial call when entering hold in the Houston TX USA area?

The same as any other area....

My step-by-step would go something like this:

Has ATC advised you "radar contact" on your flight yet?
If Yes, continue to step 2.
If No, skip to step 3.
Has ATC advised you "radar contact lost" since advising radar contact?
If Yes, continue to step 3.
If No, exit. Say nothing at all.
Say "Approach, N345 entering the hold."

My point is that in the radar environment I don't really care about you reporting established. I don't know why the AIM tells you to do it. In the non-radar environment, sure, report away... but the whole point of seeing you on radar is that I can see you on radar. I know you're in the hold because I can see it.
Either way—if you are reporting, keep it short and sweet.

However I must admit that the official FAA answer is in the AIM. Of course the AIM is not regulatory but it's generally a good idea to follow it. AIM 5–3–3a1(f) says that you should report "at all times:"

The time and altitude or flight level upon reaching a holding fix or point to which cleared.

So the by-the-book transmission would be something like "Approach, N345 entered the hold 1234 Zulu at seven thousand."


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In what scenarios would one want to maximize or minimise rate of climb in an aircraft?
What are examples of scenarios where a pilot would want to maximise or minimise aircraft rate of climb? What performance metrics should one consider to analyse steady climbing flight?
The scenarios I thought one would maximise rate of climb is military aircraft dog fight and clearance of airspace quickly in airports
Please add your thoughts if you can imagine any

Is this a homework question, or is there some underlying basis for your inquiry? There are entirely too many scenarios and variables to account for to give you a comprehensive answer unless you can narrow the scope of your question.

It's not exactly homework or assignment questions as these questions are given to us to learn more about aircraft performance and get insight about it but I can assume of only two scenarios where military aircraft dog fight and take off of commercial aircraft where one need to vacate airspace quickly . Thanks for your reply

Until I read your comment I thought you were joking. The blindingly obvious one to me is collision and/or cloud avoidance. Apparently not so obvious though. Your question would do better if you included those thoughts in your comment, people like to see what you've already thought about so they can give better answers.

@Notts90 thanks for your suggestion and can you explain why a pilot want to avoid a cloud

I'd recommend that as a separate question "What are issues with flying through clouds?". The primary is visibility, turbulence and icing are also issues.

Why would anyone ever want to minimise rate of climb?

Dogfight is about energy management. You care less about climbing than about being able to turn your nose and weapons into the right direction as quickly as possible without falling out of the sky.
Maximum climb would be required in those scenarios:

Fly as efficiently as possible. Flying higher means flying faster and in colder air, so the engines are more efficient. Note that todays airliners climb as fast or faster than fighter aircraft in WW II.
Evade ground threats. After delivering its ordnance, an attack aircraft would desire to get away from hostile fire as quickly as possible. Sometimes this is achieved by flying with the best climb angle, though.
Break off combat: If you know you can climb faster than your opponent, you can choose whether you fight or get away, a luxury the other guy does not have.
Intercept: If you were ordered to intercept an unknown aircraft flying high above, maximum climb speed is helpful. If you need to be fast as well, your optimum climb profile is that of highest energy gain, though.

I interpret minimum rate of climb as maximum descent rate. Typical scenarios are:

Pressure loss in an airliner, when higher density air should be reached in order to continue the flight safely.
Dropping parachutists: If the aircraft lands ahead of the skydivers, it can fly more often and earn more revenue.
Extreme case: Dive bombing. Actually, most dive bombers employed air brakes to limit the speed in a dive.


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Do speed and density exhibit a linear relationship?
Does speed and density scale linearly? Say you’re going 500mph, and speed up to 600mph. The density of the air will decrease.
Now if you’re going 1000mph and speed up 100mph, does the density decrease the same amount?
What is the reasoning behind the answer?

My guess of what happens with density at higher and lower speeds is the following (my guess is that it's a non-linear relationship) : The air density doesn't change much until you reach Mach ~0.3, where Bernoulli's equation isn't valid anymore, so the density can't change but so much, or Bernoulli's equation would be false, even below Mach 0.3.
When you go faster, there are less air molecules to 'bounce' off of the surrounding body and each other (because at high speed, the surrounding air is less dense), so changing speed doesn't do as much as it would at a lower speed, if that makes sense. (I might be wrong about some of those statements.)

I think if I explain my guess of why density doesn't change much up until Mach 0.3, it might clarify things. So if you have normal-density air (like still air at room temp) and you start to speed it up, a few things happen.
The air molecules bounce off of each other less, because they all have a forward speed component now, and they 'bounce' less on the surrounding container/body, both creating a lower density air. Doing this at lower speeds, there are more molecules, and because there are so many, speeding up doesn't prevent the 'bouncing' as much as it does at higher speeds. (Again, I might be wrong about some of those statements.)

Comments have been moved to chat; please do not continue the discussion here. Before posting a comment below this one, please review the purposes of comments. Comments that do not request clarification or suggest improvements usually belong as an answer, on [meta], or in [chat]. Comments continuing discussion may be removed.

I've moved the comments to chat, please continue the clarification discussion there. Once it has been clarified whether density or pressure is meant and whether we are looking at total, static or ram pressure / density, the question should be updated and flagged for reopening.

According to NASA: "As an aircraft moves through the air, the air molecules near the aircraft are disturbed and move around the aircraft. If the aircraft passes at a low speed, typically less than 250 mph, it is observed that the density of the air remains constant. For higher speeds, some of the energy of the aircraft goes into compressing the air and locally changing the density of the air. This compressibility effect alters the amount of resulting force on the aircraft since the aerodynamic force depends on the air density. The effect becomes more important as speed increases. Near and beyond the speed of sound, about 330 m/s or 760 mph at sea level, small disturbances in the flow are transmitted to other locations isentropically or with constant entropy. Sharp disturbances generate shock waves that affect both the lift and drag of the aircraft, and the flow conditions downstream of the shock wave." NASA
Updated for poster's request for "why"...
Unlike solids and liquids, a gas's molecules are loosely bound and have considerable space between them. This makes the air around us easily compressed.
As an object travels through air, the air's molecules are prevented from moving out of the way do to friction (and momentum). As an object moves faster, more molecules stack up in front of it and are kinetically forced closer together; an increase in molecules for a given space causes an increase to it's density and relative pressure.

At mach one, the air is prevented from moving out of the way at the
same speed as sound energy. Sound energy plus the density/compression
causes a sharp pressure gradient we know as a "shock wave".

Oh okay, thanks for your response. So I have a guess why the density doesn't change much below ~250 MPH, but I don't know for sure, so could you possibly explain that to me?

Why?  Because it's been measured.

I edited my question and added the last section to it, which might help you see where I'm coming from. (about the density below Mach 0.3 part)

Density is not linear to speed - there is little density increase below 250mph but disproportional to increase with speed. For example the density at 500mph is more than twice as much as 250mph. And the density at 2000mph is more than twice 1000mph. The disproportional density is primarily due to the non-linear property of friction (as explained above).

@jwzumwalt Ah okay, thanks for your help. One last thing : do you believe that my guess(es) in my question is correct? (I made a few edits and added some things)

Bernoulli's equation continues to work fine. Bernoulli is change (delta) speed vs pressure. For example water is considered uncompressible (%1<) but Bernoulli's equation continues to work, therefor it is not primarily related to density. You did make a good point that momentum is also related to the compress-ability in a dynamic situation (as is friction). My guess is friction is the major player at lower speeds and momentum plays the largest role at some point as speed increases.


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Am I correct with my thoughts of supersonic vs. subsonic flow?
So I'll just list a few things that I thought were correct. If there's anything I'm wrong about, I'd appreciate if someone could explain where I went wrong.
In supersonic (vs. subsonic) flow, the lift distribution changes because shocks form on the wing.
In places where supersonic flow would accelerate, subsonic flow will decelerate. This is due to the supersonic flow going faster over the wing. Probably sounds like a bad explanation, but I was going off of this answer.
Those probably seem very vague, but I just wanted to see if the basic principles I thought of were correct.

"This is due to the supersonic flow going faster over the wing" faster than what? Compression shocks slow down the flow, so the reverse sounds more correct.

If you’re solely concerned about wing and lift at SS, here’s a past stack answer:
In pure subsonic flow the pressure distribution is the combination of the flow around a body, where air has to speed up locally to make way for that body, and the flow around an inclined flat plate. Things will become more complicated if the rear end of the body is blunt and causes the flow to separate locally.
If you raise the Mach number, density changes will become greater and will require larger speed changes to let air flow around the body. Please remember the tube explanation from this answer to explain what happens in detail.
Things become really different once the local flow speed becomes supersonic. When before a contraction in the body would cause the flow to slow down, it will now accelerate further. This will lead to a local drop in pressure when before, at subsonic speed, pressure would increase. Eventually, this supersonic pocket will collapse in a shock, so speed drops to subsonic while pressure rises immediately. Below I copied an example of typical speed distributions from US patent 3,952,971 by Richard Whitcomb.

Speed and pressure distributions are very similar, only that pressure changes with the square of speed.
This extension of the low pressure area on the wing will shift the center of pressure backwards. If you increase flight speed further, the supersonic area will increase until at Mach 1 it will extend over the whole length of the airfoil.
On a straight wing this will happen the same way over wingspan. Only on swept wings will sweep effects make root and tip pressure distribution look different. But what happens can all be explained by the same basic principles:
-Low pressure areas suck in more air, so they attract the flow.
-Conversely, high pressure areas will divert the flow.
-At subsonic speed air needs to speed up to make way for the airplane.
-At supersonic speed air needs to slow down to make way for the airplane.

Welcome Nick.  If you are quoting someone else's writing, please add complete attribution.

Lift doesn’t change significantly. Drag does though. The complicated part of supersonic flight is not wing design, but rather controlling the speed at which the air enters the engine/intakes, which is why most SS aircraft feature variable intake angles.

Welcome Nick. Although "complicated" is subjective, optimal wing design for supersonic vs. subsonic flight is quite different.


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How does flight duration affect the hourly fuel consumption in heavy aircraft?
A 15 hour flight across the Pacific obviously requires more fuel than a 7.5-hour transatlantic flight.  How significant is the hourly fuel consumption increase due to the additional fuel carried at the beginning of the longer flight? Another way of asking the question would be: How much more more fuel do you need to carry (in a typical heavy plane such as the B747-400) for a flight that is twice as long?

You could take the Breguet range equation to derive some of those numbers, at least approximately. Including takeoff&climb will be complicated (and depend on more variables).

@yankeekilo: care to write an answer based on these equations (w/o including T/O and LDG)? Otherwise I might take a shot at it...

Please be my guest,  in fact I was hoping for those very words :D

General Answer
The heavier the airplane, the more fuel it will burn in a given amount of time.  Therefore, if you takeoff with enough fuel to fly further, you will be burning more fuel in each corresponding hour than if you took off at a lighter weight to fly a shorter distance.
Example
I don't have performance information for the 747, but I can give you an example for a G-IV corporate jet.  Instead of comparing a short trip to a longer trip, I planned the same trip with different amounts of fuel in order to make the airplane heavier.  I planned the flight for the following conditions:
Flight Conditions

Fly from Los Angeles to Detroit, using the same route and average Boeing winds for July
Climb to and maintain the optimum altitude, with step climbs where appropriate

Trip 1: Climb initially to FL450 and stay there for the entire flight (the optimum altitude for this weight)
Trip 2: Climb initially to FL410 and then climb to FL450 2:32 into the flight (the optimum altitude the weight initially followed by a climb once the optimum altitude has changed)

Fuel:

Trip 1: Takeoff with enough to land with a 1:30 reserve - 59,000 lb. takeoff weight
Trip 2: Takeoff with max fuel, landing with a 5:39 reserve - 73,000 lb. takeoff weight
Taxi fuel is not included in the first hour burns, but climb fuel is.

Results
          Trip 1      Trip 2
Hour     Fuel Burn    Fuel Burn     Diff
 1        4,212         4,844      +13.7 %
 2        2,536         3,088      +21.8 %
 3        2,411         3,123      +29.5 %
 4        2,163         2,103      -2.8 %
 Total    11,722        13,558     +15.7 %

Summary
As you can see, the fuel burn is significantly higher in the first 3 hours due to the additional fuel that we were carrying (and therefore the higher weight of the aircraft).  Hour 4 is almost the same because of the idle power descent used in the planning software.

When you say "Climb initially to FL450 and stay there for the entire flight". What does FL450 means?

@GabrielBrito FL450 stands for "Flight Level 450" which is (roughly) 45,000 feet.  You convert a flight level to feet by multiplying by 100.  The one major difference in aviation though is that a flight level is not corrected for local pressure variations while actual altitude would be.  So it's "close" to 45,000 feet in this case.

Another consideration is the fact that the center of gravity changes as the fuel burns.
Yet another is whether you have ballast fuel, fuel used to bring the zero fuel weight c.g. within the allowable envelope. Technically speaking, ballast fuel is not available to burn, although obviously if that's all that's left you're going to use it.
Then there's the matter of extra fuel to make a captain happy that's above what the flight planned fuel is. Let's say the captain wants 8,000 lbs of extra fuel. For the old 747-100 and -200 aircraft, the rule of thumb was that if you loaded extra fuel, 20% of that fuel would be used just to carry it. In other words, If you wanted an extra 8,000 pounds available, you needed to load 10,000 extra.
Another rule of thumb for the old 747s that was used as a check on whether the fuel called for in the flight plan was reasonable, was to figure 30,000 lbs burns for the first two hours, 25,000 lbs per hour after the first two.
Unfortunately I no longer have the manuals for the 747 that would allow me to accurately compare, say, a four hour flight against an eight hour flight.

On the 747-400, the general rule for extra fuel used to carry extra fuel was 4% per hour or 3% per hour depending on your requirement.
If you wish to arrive with 10,000 pounds extra after a 10 hour flight you would have to load 14,000 pounds extra before departure (the 4% rule)
If you load 14,000 pounds extra before departure for the same 10 hour flight, this is burnt at 3% per hour (the 3% rule) leaving you with about 10,000 pounds at arrival.
The sums:
$$10,000\times4\%\times10hours=4,000lbs~burnt$$ to carry it, so load 14,000 pounds.
$$14,000\times3\%\times10hours=4,200lbs~burnt$$ to carry it, leaving 9,800 at the destination.
Close enough for Government work!

Just to put this in perspective, he was asking about catering an extra 7.5 hours of fuel. How much would that be, and how much does that increase the fuel burn overall during the first hours when it is extremely heavy?

For every 1% reduction in fuel weight there is a .75% reduction in fuel burn, "it takes fuel to carry fuel"


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Why is TALPA not used for take off? Why is it used for landing?
TALPA - Takeoff and Landing Performance Assessment has been introduced. What is it exactly and why is it not used for take-off, when it is stated in the name TALPA?

If you don't know what it is, then how can you be certain what it is or isn't used for?

I think TALPA is now replaced by ICAO defined Global Reporting Format (GRF). For landing performance assessment the RWYCC (0-6, average of the last two thirds of the runway) is sufficient. For takeoff performance assessment you need also the thickness and type of the thickest contaminant on the runway.


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Operating with BasicMed, may pilot use a medication otherwise restricted under Part 67 Medical Regulations?
I have a CFI student who is currently using BasicMed to satisfy her FAA Medical Requirement.  She is taking a drug, which the FAA in AME guidance prohibits, and is wondering if she can continue to take that drug.  Going through the regulations, there is no FAR specifically naming drugs, and it appears that for BasicMed, the approval for drug use lies with the examining/issuing physician.
She has gone back to her (issuing) physician and verified that there is no concern with her taking this drug while operating a "vehicle or aircraft" and the physician has confirmed that in the physician's opinion there is no concern.  In her case, her primary care physician (PCP) declined to provide a BasicMed exam, but her endocrinologist agreed to. The drug in question is one the endocrinologist is using to treat her with.
So what we have is a situation where the AME's receive guidance to "Do Not Issue" (DNI) and under BasicMed it appears that the issuing physician can decide contrary to FAA Class 1, 2 or 3 policy.  The question is: Under BasicMed may a pilot be taking a drug, with the approval of their physician, which would otherwise be prohibited under a Class 1,2 or 3 FAA medical?
Addendum: The following is a AC issued shortly before this question was asked:
https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_68-1A.pdf

Does your student already have an FAA medical?

She holds a current Class 1 medical, but does not exercise that medical due to a new diagnosis, and Rx treatment.  She also holds a BasicMed medical which she intends to use while on her current treatment.

New opinion. Met with former CFI student, now MD, who reviewed BasicMed rather throughly, and also has the opinion that physician can approve meds that the FAA does not, as long as there is not a cardiac, psych or neuro disease. Another data point.

I wonder what he considers a psych disease. Do you suppose stuff like depression and ADHD count? This big streaming pile that is BasicMed helps some people, but didn't help me at all.

I can ask him. I would urge you to carefully read the regs, as well as the enacting legislation. ADHD is at first blush not disqualifying, but the medication could be.  Just first blush.

Oh, I'm well versed on the regs. But you never know how a doctor, an AME or the flight surgeon is going to interpret them. With the 3rd class "reform" the catch is that a new pilot still has to get a 3rd class med. In my case I'd have to go off my banned meds for 6 months, then jump through all the costly hoops to get a special issuance. After that BasicMed would be great. I've done enough ranting on av.se about the FAA's medical requirements. The reform bill gave me hope. BasicMed dashed that hope.

Looking at section 2307 of H.R.636, which is the congressional bill which implemented BasicMed requirements, it is clear that the physician who performs the exam, and provides care to the subject is responsible for determining what drug interactions there might be, as well as the impact of medical conditions, and whether they might be disqualifying.
Armed with this, my CFI student and I called a friend who is with FAA counsel, who does not address airmen issues, but rendered the opinion that BasicMed is separate from FAA Class 1, 2 and 3 medicals.  It is separate from Sport Pilot medicals. It is unto itself. Therefore it is their opinion that it was the legislative intent to create a separate certification process.
Therefore, the examining/issuing physician makes the determination as to any medical conditions or drugs and their impact on flying. He is the subject matter expert, and therefore if full disclosure is made, the airman has operated in good faith.
Of course, we were invited to submit an interpretation request, so that we could get an official response.
When talking with attorneys, and especially FAA attorneys (in their unofficial capacity) there many disclaimers, which include neuro, psych and cardio prohibitions.  And the importance of consultation with the issuing physician when there are medical changes.


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Do some aircraft now have "full aircraft" parachutes?
I was intrigued to see this mentioned in passing,
https://web.archive.org/web/20160824204313/http://robbreport.com/aviation/cirrus-aircrafts-vision-sf50-personal-jet-completes-flight-testing-video
Is it true that some new products now have this?
Do they actually work, are there any demo videos, who pioneered it, in what situations is it actually useful, etc?

heavily related http://aviation.stackexchange.com/questions/593

http://www.theguardian.com/world/video/2015/nov/03/plane-parachutes-to-safety-on-arkansas-road-video

Yes, Ballistic Recovery Systems or Ballistic Parachutes (BRS) are now being implemented in newer aircraft where the manufacturer can provide them or where they are required by law. In Germany, Ultralights are required to have an installed BRS to be deemed airworthy.

In Europe the sporting (FAI) definition limits the maximum take-off weight to 450 kg (992 lb) (472.5 kg (1,042 lb) if a ballistic parachute is installed) and a maximum stalling speed of 65 km/h (40 mph).

The general idea is to allow the airframe to glide down to the surface and being attached to the airframe, the time saving for pilots to otherwise have to jump out and open their own parachutes (if equipped) is substantial.
The first parachutes were used by Comco in 1982:

In 1982 Comco Ikarus developed the FRS rocket-launched parachute system for its ultralight and hanglider aircraft.2 In 1998 Cirrus Aircraft provided the first ballistic parachutes as standard equipment on their line of type certified aircraft, the Cirrus SR20.

(Image Source: WikiMedia Commons - Author: NASA)
Here is a Video of the Cirrus Airframe Parachute System in action:

(Image Source: YouTube - Author: AIRBOYD)

An entry on www.aviation-safety.net about the Cirrus parachute system:

The aircraft experienced a deployment of the Cirrus Airframe Parachute System (CAPS) over west Fayetteville, Arkansas. The airplane came to rest on a roadway shoulder sustaining substantial damage. There was 4 occupants on board, at least two people taken to the nearest hospital with minor injuries, according Police Department.
  The plane started having oil pressure issues immediately after take off.

Holy!  that video is of an actual real-world use.  (Ferry pilot had no fuel due to valve malfunction?)

Yeah, the parachutes are actually functional and are used where required. They are not cosmetic. ;)

thanks, amazing .. up to what speed can such a device be deployed??  (Do you have to, perhaps, first deliberately stall the aircraft, or some such, depending on the nature of the emergency?!)  Amazing.

Right on. At first I assumed the video was from the company -- a deliberate test.  But it's a real rescue, video'd by the Coast Guard.  Wow!  I wonder if the system would be useful even in low-altitude disasters (near take-off etc)?  (Much as current advanced ejector seats for single-seaters, would amazingly appear to be helpful even in near-the-ground situations, as I understand it from seeing "spectacular videos" online.)  or is the Cirrus system only for, when your Cirrus fails at a fairly high altitude?  (Perhaps a few 1000 feet?)

@JoeBlow there is a envelope (height/speed) where the parachute deployment is best, it's not stall but below 200 knots $V_{ne}$ and above 1000 feet AGL

Totally amazing.  thanks.  Only 1000 feet!  I wonder how they thought-out avoiding tangles on the tail, it looked like a close-run thing there for a second when the device was deploying!!

@ratchetfreak: Granted, a couple of successful deployments have occurred even above V-NE and/or below 1 kft AGL.

For gliders, the first BRS was used in the experimental flying wing SB-13. Since the pilot was placed in a cockpit much larger than the wing, the fairing in his back was mostly empty. This space was used to house three parachutes and a spring-activated small extraction chute. The system was first tested on a 1:3 scale model (picture below).

Model test of the SB-13 parachute rescue system (own work)
Later, the full-size system was tested with the cockpit section alone. The mass of the wings was simulated by stacks of steel plates bolted to the sides of the fuselage. The picture below shows the test with three chutes; the small spot on the left is the lid of the parachute compartment falling away.

SB-13 full scale drop test in 1989 (own work). The fuselage was lifted aloft by a helicopter and then dropped. The added tail surfaces made sure it fell nose down.
On the last test someone (not me!) forgot to switch on the receiver in the fuselage, so the parachute was never released. The fuselage was completely destroyed and the steel plates dug themselves so deeply into the soft ground that they were never found. We stopped digging after less than a meter, though.
A second test fuselage was built to complete the test series of 12 drops, including an instrumented dummy in cooperation with TÜV Rheinland to measure deployment and impact stresses, which were determined to be survivable without serious injuries.
The parachutes can be activated over the full speed range, however, at high speed the deceleration is quite severe. The riser lines are woven and will stretch under load, so the peak acceleration can be reduced. This means that the lines can be used only once. After activation, new and unstretched lines need to be fitted to make the system airworthy again.

Amazing experience commentary, Peter, thanks!

Isn't the airframe ALSO done after one use of the BRS?

@RalphJ: At least the landing gear and whatever hits the ground first. Even if no external damage is visible (unlikely - impact speed is around 7 m/s) a thorough check is needed. To reduce the impact shock for the occupants, it can be helpful to hoist the aircraft asymmetrically, so one wingtip will hit the ground first. The other wing will then still be usable ;-)

Hey Erpel: Der Smiley hatte echt vergessen, den Empfänger einzuschalten. Bitte jetzt nicht nachträglich die Geschichte neu erfinden. Das passiert schon häufig genug, aber nicht in meinen Antworten. Da steht das, was wirklich geschah.


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What is the difference between a spin and an uncontrolled roll in an high speed dive?
A comment I had on another (now deleted) question states that China Airlines 006 didn't spin. For me it was a spin (unwanted roll due to asymmetrical stall). The comment states it was "it was a slow roll during a very-high-speed dive".
How can I make the difference between both? What makes this occurrence of uncontrolled roll not a spin?

I believe the key difference is that a spin occurs due to a stalled wing and consequential instability in the longitudinal axis. Wheras “uncontrolled roll” may occur in a non-stalled condition - maybe a spiral dive well beyond Vne with no aileron command authority.

How can I make the difference between both?

The main difference between a spin and a spiral dive is in the angle of attack (much higher in a spin) and, consequently, much less drag in case of the spiral dive which results in higher speed.

What makes this occurrence of uncontrolled roll not a spin?

Both can be entered from an asymmetric stall. When the cg is more forward, a spiral dive becomes more likely and vice versa. Some airplanes will only enter a spin with a rear cg location and must be held in the spin with rudder in spin direction and stick back. Other airplanes will still spin with controls neutral, and the cg location has a high influence on how easy it is to end the spin.
All symptoms look like the Air China 006 upset was a spiral dive.

In the beginning of the article on Wikipedia it is stated that the plane experienced "high G forces and high speed". Not knowing the story of the flight but with this statement we can suppose that it wasn't a spin but rather a spiral dive. But when reading the full story it is stated that the lose of engine 4 leads to a decrease of the speed, that the pilot didn't had any rudder control, applied full left yoke and yet the airplane was still rolling right. Those are clear sign of a spin and not a spiral dive!!
A spin begin in situation where asymmetric stall occurs. In this situation the airplane start spinning on the yaw axis, the external wing creates more lift wherase the inner wing is stalled and drops, thus driving the nose down. But the main characteristic in a spin is that your airspeed is very small (which doesn't mean that the sink rate is not high) but prevent extreme aerodynamic loads on the aircraft and the g loading remain somewhat close to one during the spin. In one word the airplane is falling vertically from the sky spinning on itself, wing inclination can be close to 0 up to 90° depending on the aircraft.
On the other hand a spiral dive can occurs without any stall. When starting a turn if you let the nose drop, the inclination will increase and your speed will increase. At one point pulling on the yoke will only  tighten the turn and increase g forces but will not move the nose up. This situation can happen when you're focused on something on the ground and start turning to see it better. If you don't pay attention the nose will drop and it's a one way trip as you are focused on the ground and not your instruments. You reach VNE and loose control of the aircraft. In this situation the aircraft is flying a tight spiral to the ground with high wing inclination always increasing which can be seen as a slow roll.
In a spin you mostly use your rudder pedal to stop the rotation and then pull on the yoke wherase in a spiral dive you need to use the yoke to reduce inclination first and then pull. Adding some yoke to stop rotation in a spin will not help and worse may even flatten it and increase rotation speed. Using rudder pedals in a spiral dive won't have much effect, you need to bring down the inclination, level the wings and this is mostly done using the yoke while keeping your flight coordinated with rudder input if needed. Therefore it is important to differentiate both situations if you want to come out of one of them alive.

With high wing loading and low air density, even a spin leads to very high sink rates. Also, the high roll rate in a spin can easily overstress the wing tanks due to centrifugal loads. Don't underestimate structural loads in a spin!

Yes correct, in spin you will have a high sink rate, same as for spiral dive in any airplane.  My experience comes from aerobatic flying and centrifugal loads are not really a concern there. What is sure is that your airspeed is not increasing in a spin (outside of the recovery dive) and that's why I was stating that you might not overstress the aircraft... But for an airliner the story might be different you're correct.

A spiral dive produces MUCH less drag and speed buildup is massive and massively dangerous. A spin is comparatively harmless and the most likely reason that Air China 006 came down in one piece. The high initial speed can be explained by low density and maybe incipient spin particularities of the B747. I've never spun one myself, so I am guessing here.

Yes that's pretty much what I'm saying no?

You say "… I suppose that it wasn't a spin but rather a spiral dive". I disagree.

The question was why they don't speak of stall on the Wikipedia page and for me the answer is because they are wrong. A spiral drive would have probably leads to excess VNE, increase aerodynamic loads an rip wings of the airplane.

Ho, maybe my edit section at the top of the answer was not clear enough, I posted the answer not knowing the story of this flight and the statement high G and excessive speed leads me to the conclusion of a spiral dive. After reading more they had slow speed, no rudder control and full left yoke while rolling to the right so that's definitely a spin and I added that on top. Will modify again to make it clearer but we're on the same page!!

@MaximEck it's not really a spin until the aircraft has stabilized in an autorotation, descending more or less vertically (an autorotation while going horizontally is a snap roll).I don't think this incident counts as a spin event as in a fully developed autorotation.  It was a combination of incipient spin at the start (roll off with some yaw), followed by a disoriented pilot pulling this way and that in various corkscrew like maneuvers.There was a CRJ200 crash in Scandinavia where capt became disoriented and rolled and dived and went every which way, before hitting the ground at 500 kt.

@MaximEck  in a spiral dive the rudder petals absolutely help, along with the throttle.  Reducing throttle, and a coordinated turn out of a spiral dive would be my approach, followed by a careful pullout.  Not good to get uncoordinated close to Vne.

@JohnK A spin needs at least three rotations to fully develop in such a large aircraft. All before is called "incipient spin" and might very well include a vertical dive, combined with a rolling motion. This rolling motion needs to build up so the inertial loads on the fuselage will allow the high AoA of a spin to stabilize.

@Robert DiGiovanni the faster you fly the less rudder application is needed to keep your turn coordinated. But your answer is totally correct, reduce trotel, level wings and carefully pull out. My point was that rudder alone won't help in a spiral dive. As the aircraft is still flying, classical action are still valide. The opposite is not true for a spin, adding some ailerons will rarely help and most of the time the situation will get worse.

There has been plenty written about that B747 incident. I have seen a re-creation in a simulator. For aspiring airline pilots suffice it to say that in any abnormal situation someone has to fly the aircraft. You know, the basics….
He or she has to keep a safe airspeed and if an engine is lost at high altitude that will mean starting a descent. The yaw will have to be countered by applying some rudder. Wings level, ball in the centre. It is called flying.
Then while someone is flying, the other(s) can open the book, try to restart or secure, consider terrain, alternate airports, get on the radio etc etc.
For student pilots, you will be shown what a spiral dive looks like; increasing airspeed and bank angle and high rate of descent. Reduce power, level the wings and ease out of the dive.
You will have to demonstrate the same recovery prior to getting an instrument rating without outside reference. You will also have to demonstrate remaining in control, by hand and foot following engine failures in multi engined aircraft, securing the engine by following some procedures by memory. This will have to be done on instruments without outside reference for multi engined instrument ratings.
Wings level, ball in the centre, maintain correct speed, get rid of drag (landing gear) etc dead foot, dead engine etc etc.
It is called flying.
You will be shown how to recover from a stall and how not to get into a spin.
You can also get spin training. In a spin the airspeed starts low and stays low.
Some aeroplanes can be gotten into a spin but will not stay there long - they can transition into a spiral dive, airspeed increasing etc as above with the same recovery.
I think this is what happened to that 747. The pilot flying let the airspeed decay and did not counter the asymmetry with rudder. The a/c stalled and a wing dropped. The aircraft then transitioned into a spiral dive.
In the re-creation I saw both Captain and FO thought that their respective Attitude Indicators had failed simultaneously when the wing dropped! “I lost my horizon!” “I lost my horizon too!”
Luckily the cloud base was high enough for them to recover when visual reference was gained. But high g was put on the airframe and bits and pieces came off in the process.
Remarkable aeroplane the Boeing 747!

Perhaps it was in a spin for some time, but IMHO, I don’t think that it could stay stalled and spinning without pro-spin controls held.


text:
How feasible is it to sell a plane with an expiring annual?
I'm preparing to sell my plane, an IFR-equipped, low-time, C150E, but the annual expires at the end of this month.
What's the best course of action?  I know that if I was buying a plane, I would love it if the annual was just expiring - I'd just do a full annual as a pre-buy inspection on the condition that the seller paid for anything non-airworthy.  I also know that a lot of people prefer to sell planes with fresh annuals.
What's the best approach here?  And what happens if the annual expires?  Will that hurt my chances of selling the plane?

I'm not sure if this is a question that fits stack or not.  My opinion on the subject is that if I were buying a plane, I would feel more comfortable if the annual were completed just prior to the sale and that all required repairs were made by the seller.  I don't think letting the annual lapse will hurt as long as it doesn't go on for some terribly extended period of time that would require the engine to be pickled or something.

Out of annual = can't fly it home = barrier to entry.

I also know that a lot of people prefer to sell planes with fresh annuals.

I think the reality (from what i have seen) is that a a lot of people end up selling planes with a fresh annual. Essentially any smart buyer is going to want a pre-buy inspection and they are often willing to pay for them. In many cases pre-buy inspections are close to if not the same as an annual so the mechanic will often do the remaining work and sign it off as an annual resetting the clock. Any potential buyers are going to want to test fly the plane so its going to need to be air worthy. I would suspect the soon expiring annual has a small impact on price (in and around the cost of the annual which is comparatively low for a 150).
You may find a buyer fast and unload the plane while its still airworthy, taking a bit of a  hit for the soon to expire annual or you may get it done and raise the price close to the cost of the annual.

It's fine.  A buyer will make their prebuy an annual.  I would negotiate a lower price from you because an annual is necessary in this case where it may not be otherwise.
Realistically, when I look at planes, the annual status is irrelevant.  I'm going to get in there and check things to make sure everything is as it should be.


text:
I want to find out more about Raab Schwalbe Reg SX-AAG
According to the records on the web, Raab Schwalbe 11 reg SX-AAG was built in Greece in 1935 and sold abroad in 1937.
I know that it was destroyed in a crash on landing in Palestine but I am not sure when that happened.  I originally thought it would have been in 1936 but it may have been later. The picture was taken in Palestine before it crashed.
Does anybody know more about the history of SX-AAG?

Could you summarize which sources you have already consulted in your search for information?

The only information I found on the web came from http://www.airhistory.org.uk/gy/reg_SX-.html


text:
Why do we not have autonomous helicopters?
We see a lot of fixed wing autonomous UAVs. What is preventing this in the case of helicopters?
I know the helicopter flight dynamics are complicated. But what exactly is the complication in this case?

"We see a lot of fixed wing autonomous UAVs" - do we? Where? You realise the millitary UAVs that you're perhaps thinking of have 2 flight crew sitting on an unnamed base somewhere half way round the world, right? Furthermore, most Actual autonomous UAVs are drones... which are probably closer to helicopters than fixed wing aircraft.

Yes even they are not autonomous in the true sense of the word. But fixed wing autonomy is possible. The challenges it faces are different and are being worked upon. When it come to helicopters, they are not even as popular as the so called autonomous fixed wing UAVs. Hence the question.

I have never, not once, ever, seen an autonomous UAV.

I guess the OP has never seen this thing either: https://en.wikipedia.org/wiki/Kaman_K-MAX

Multirotor autonomous craft are making headway.
Here is one named Vahana that was in the news recently. The Vahana link has video too.
https://media4.s-nbcnews.com/j/newscms/2018_09/2345131/180228-vahana-air-taxi-main-art-mn-1210_ebe3af14b2fcd27626c26bd127203e22.focal-1000x500.jpg
Here is another being tested in New Zealand
https://ichef.bbci.co.uk/news/660/cpsprodpb/18433/production/_100397399_mediaitem100397398.jpg
Google "airtaxi" and there are many links to companies like Uber that have plans and visions for autonomous airtaxi service.  Some have scale mockups, some have just pictures.
I haven't seen any plans for autonomous helicopters, only multirotor vehicles. The multirotor vehicles give you a chance at recovery should one motor be lost; a helicopter, not so much.

Don't we? Most consumer and commercial UAV are helicopters.
If you mean military-only models, consider what jobs military-only helos do. It's troop transport or close combat - both necessarily manned functions. Commercial drones suffice for non-military-specific jobs.
If you wonder why they have 4 rotors rather than 1-2, it's lower complexity - quads can use simple fixed rotors and blades, and only vary power on each rotor. Larger drones with turbine power may well go to 1-2 rotors.


text:
What was the value proposition of the 767-400ER over the 777?
Aside from visible differences, what are some differences in the usage and design of the 767-400ER as compared to the 777-200/200ER (or 300/ER if you feel makes more sense)?
What was the value proposition of the 767-400ER when compared to the 777, as both came into service within a decade of each other?

It's pretty clear that operators of the 767-400ER knew what they were doing when they selected that aircraft. Only United and Delta bought them and they are still in service even as older 767 models are being retired. The 764s have proven to be a good value proposition even though it did not sell well and is a unique bridge between smaller and older 767 models and the much larger 777s, especially when you examine passenger cost and revenue per mile.
They have been particularly useful for transatlantic service, and both United and Delta plan to fly them for at least ten more years -- and they've both decided to spend millions on them to upgrade their interiors to maintain parity with newer Airbus and Boeing products. It appears that both airlines are planning to keep them going until Boeing introduces the NMA (797). I hope that's what happens because there's no question that passengers greatly prefer two aisle aircraft over single aisle competition such as the A321LR or the A321XLR for seven to ten hour flights.
I still prefer the 777 over the 767-400 but can see why United and Delta continue to fly 764 over single aisle aircraft or a larger aircraft that does not sell out on the same length flights.

Two aisles are indeed more comfortable, it feels like you have more room, you can stand up and walk a round and boarding is faster.

I take value proposition to mean criteria used by a purchaser to determine which aircraft to buy. Excluding financing deals and fleet commonality, the main criteria used when purchasing an aircraft are capacity, range, and seat mile cost.

3 class capacity of the 767-400 is 243 vs 301 in a 777-200er.
range is 5600kt vs 7000kt respectively.
seat mile cost is 7 cents vs 7.5-9 cents respectively. source

Seat mile cost is trickier as airlines do the reports and they use different criteria. You would think that a larger plane would have lower seat mile costs, but configurations differ between aircraft, airlines, and trip length. You are also looking at the largest model of one series, usually the most efficient, and comparing it to the smallest of another, usually the least efficient. It's kind of a mess and the manufacturers argue about this all the time.
The upshot is that the 767-400 is better for thinner (lower passenger demand), shorter routes and the 777-200er is better for longer, thicker routes where the increased cost matters less, as the 767-400 can't do the job.

"You would think that a larger plane would have lower seat mile costs" Assuming you can fill them without reducing ticket prices, that is.

@reirab Seat mile cost is independent of revenue. Sorry for the slow response.

I think the only airlines which would have considered a 767-400 is one which already has 767s in the fleet. And even then it would be a product at the end of its life-cycle so fleet renewal considerations would play a part.